Japanese Patent No. 2544815 discloses a level shift circuit monolithically formed in a one-chip IC that can shift both the high voltage level and the low voltage level of an input voltage.
This prior art level shift circuit includes an initial stage circuit portion, a first intermediate stage circuit portion, a second intermediate stage circuit portion and a final stage circuit portion and is formed monolithically in a one-chip semiconductor integrated circuit. The first stage circuit portion includes an inverter connected to a first high potential power source (+5 V) and a first low potential power source (0 V) and provides, in response to an input signal, an output voltage whose H level is the voltage level of the first high potential power source (+5 V) and whose L level is the voltage level of the first low potential power source (0 V). The first intermediate stage circuit portion includes an inverter connected to the first high potential power source (+5 V) and a second low potential power source (−10 V) having a voltage level lower than the voltage level (0 V) of the first low potential power source and provides, in response to the output voltage of the first stage circuit portion, an output voltage having the logic state opposite to the input signal with the H level being the voltage level of the first high potential power source (+5 V) and the L level being the voltage level of the second low potential power source (−10 V). The second intermediate state circuit portion includes an inverter connected to a second high potential power source (+10 V) having a voltage level higher than the first high potential power source (+5 V) and the first low potential power source and provides, in response to the output voltage of the first stage circuit portion, an output voltage having the logic state opposite to the input signal with the H level being the voltage level of the second high potential power source (+10 V) and the L level being the voltage level of the first low potential power source (0 V). The final stage circuit portion includes an inverter connected to the second high potential power source (+10 V) and the second low potential power source (−10 V) and provides, in response to the output voltage of the first intermediate stage circuit portion and the output voltage of the second intermediate circuit portion, an output voltage having the logic state same as the input signal with the H level being the voltage level of the second high potential power source (+10 V) and the L level being the voltage level of the second low potential power source (−10 V).
With development of micro-machining techniques, the importance of actuators has been growing in various fields. An example of the fields in which micro-actuators are used is an optical switch that is used in optical communications, etc., to switch optical paths. Such optical switches are disclosed for example, in Japanese Patent Application Laid-Open Nos. 2001-42233 and 2003-334798.
In the optical switches disclosed in Japanese Patent Application Laid-Open Nos. 2001-42233 and 2003-334798, micro-actuators for moving micro mirrors are used. The micro-actuator has a movable portion that is movable relative to a fixed portion, and the movable portion is adapted to be returned to its upper position (at which the micro mirror can reflect incident light) by a spring. In addition, a first electrode portion (fixed electrode) is provided on the fixed portion, and a second electrode (movable electrode) is provided on the movable portion. A voltage is applied between the first and the second electrodes to generate an electrostatic force between them, whereby the movable portion is brought to its lower position at which the micro mirror leaves incident light to pass while intact and maintained at that position. When application of the voltage between the first and the second electrodes is stopped, the movable portion is returned to its upper position by the spring.
The level shift circuit disclosed in Japanese Patent No. 2544815 includes two circuit portions in the intermediate stage (i.e., the first and the second intermediate circuit portions), and a large number of elements such as MOS transistors are needed in that circuit. Accordingly, it has been difficult to miniaturize it, and it has suffered from low production yields.
Furthermore, the level shift circuit is required to have a relatively large difference between the high potential level and the low potential level of the input voltage in some cases depending on the use. In such cases, the level shift circuit is required to have a high withstand voltage. For example, in the case where a level shift circuit is used, in order to control a micro actuator utilizing an electrostatic force like those adopted in the optical switches disclosed in Japanese Patent Application Laid-Open Nos. 2001-42233 and 2003-334798, to supply a voltage between the movable electrode and the fixed electrode, a relatively high voltage is required, and therefore the level shift circuit is required to have a relatively high withstand voltage.
Furthermore, the level shift circuit is demanded to be simple in the structure and easy to manufacture as is the case with typical semiconductor devices.